Back-up pressure intensifier for master cylinder failure

Abstract

A braking unit includes an intensifier mechanism for intensifying a braking liquid pressure of a master cylinder upon failure of a liquid pressure booster. The braking unit comprises the intensifier mechanism for intensifying the braking liquid pressure of the master cylinder when actuated, and a control valve which makes the intensifier mechanism operable upon failure of the liquid pressure booster. The control valve comprises a valve member which is urged by a spring tensioned with a given load and which is urged in the opposite direction from the spring by a liquid pressure of a power chamber of the liquid pressure booster. The valve member makes the intensifier mechanism operable whenever the resilience of the spring exceeds the urging force produced by the liquid pressure in the power chamber of the liquid pressure booster. This prevents an operational lag of the intensifier mechanism in the event the liquid pressure booster fails.

What is claimed is: 
     
       1. An intensifier assembly for a vehicle braking unit, the braking unit including a booster connected to a brake pedal to boost a braking liquid when the brake pedal is depressed, a master cylinder connected to the booster to receive the boosted braking liquid from the booster and to generate a pressurized braking liquid for application to a wheel cylinder in response to receiving the boosted braking liquid, said intensifier assembly including: an intensifier unit including: a casing, said casing being shaped to have an inlet through which pressurized braking liquid from the master cylinder is received and an outlet opposite said inlet through which braking liquid is discharged to the wheel cylinder;   a movable piston disposed in said casing, said piston having a front end located adjacent said casing inlet and a rear end located adjacent said casing outlet; and   a biasing mechanism extending between said casing and said piston for urging said piston towards said casing inlet; and     a control valve disposed in said piston for controlling actuation of said piston, said control valve including: a fluid passageway formed in said piston so as to extend between said piston front end and said piston rear end so as to allow braking liquid flow through said piston;   a valve member slidably movable in said piston, said valve member having a valve seat disposed in said fluid passageway and movable between a open position for allowing braking liquid fluid flow through said fluid passageway and a closed position that blocks braking liquid flow through said fluid passageway;   a pressure chamber formed in said piston around said valve member by at least one surface of said valve member and connected to receive boosted braking liquid from the booster, said pressure chamber being positioned so that when the boosted braking liquid is applied thereto, said valve member is urged towards said valve seat open position; and   a spring disposed in said piston and positioned against said valve member for urging said valve member towards said valve seat closed position, said spring being configured to operate in opposition to said force imposed by the boosted braking liquid in said control valve pressure chamber so that when the force of the boosted braking liquid falls, said spring urges said valve member to said valve seat closed position.     
     
     
       2. The intensifier unit of claim 1, wherein: said intensifier unit piston has a stepped configuration having a large diameter section location adjacent said casing inlet that forms said piston front end and a small diameter section integral with said large diameter section, said small diameter section being located adjacent said casing outlet and forming said piston rear end; and   said casing is formed with a large diameter bore in which said piston large diameter section is disposed and a small diameter bore contiguous with said small diameter bore in which said piston small diameter section is at least partially disposed.   
     
     
       3. The intensifier assembly of claim 2, wherein said intensifier unit biasing mechanism is a spring, said intensifier mechanism spring being configured to extend between a surface of said casing defining said large diameter bore and said piston large diameter section. 
     
     
       4. The intensifier assembly of claim 2, wherein said intensifier unit biasing mechanism is a spring, said intensifier mechanism spring being configured to extend between a surface of said casing defining said small diameter bore and said piston small diameter section. 
     
     
       5. The intensifier assembly of claim 1, wherein said intensifier unit biasing mechanism is a spring. 
     
     
       6. The intensifier assembly of claim 1, wherein said valve seat of said valve member of said control valve is a ball mounted to said valve member. 
     
     
       7. A braking unit including: a master cylinder for applying a braking liquid pressure to a wheel cylinder;   a liquid pressure booster disposed between a brake pedal and the master cylinder for boosting a force with which the brake pedal is depressed upon depression of the brake pedal at a given ratio before it is transmitted to the master cylinder;   an intensifier mechanism disposed in a braking liquid path which provides communication between a wheel cylinder and the master cylinder that is adapted to be actuated to intensify the braking liquid pressure of the master cylinder for transmission to the wheel cylinder; and   a control valve assembled into the intensifier mechanism for actuating the intensifier mechanism upon failure of the liquid pressure booster or a source of liquid pressure associated therewith wherein: the intensifier mechanism includes: a stepped piston slidably fitted in a liquid tight manner in a stepped through-bore formed in a casing;       a first pressure chamber formed within the casing adjacent to a large diameter portion of the stepped piston and communicating with the master cylinder;   a second pressure chamber formed within the casing adjacent to a small diameter portion of the stepped piston and communicating with the wheel cylinder;   a third pressure chamber formed within the casing at a location opposite to a stepped end face of the stepped piston and communicating with either a power chamber of the liquid pressure booster or a source of liquid pressure associated with the liquid pressure booster; and   a return spring disposed in the casing for returning the stepped piston to its operative position; and   the control valve includes: a first communication path formed within the stepped piston for providing a communication between the first pressure chamber and the second pressure chamber;   a sliding member slidably fitted in the first communication path, the sliding member including a large diameter portion at a median portion along the length thereof and having one of its axial ends facing the second pressure chamber through the first communication path and having the other end disposed to face the first pressure chamber through the first communication path;   a second communication path axially extending through the sliding member;   a valve element disposed on the end of the second communication path which is located adjacent the first pressure chamber so as to be movable lengthwise along the second communication path, the valve element being urged by a first spring disposed within the second communication path toward the outside of the second communication path;     a stop member disposed on the sliding member at a location adjacent to the valve element for preventing the valve element from projecting outwardly beyond a given amount from the second communication path;   an annular valve seat formed in the first communication path so as to be located opposite to the valve element and allowing the valve element to be seated thereon;   an engaging member disposed within the first pressure chamber and including a distal end which extends into the first communication path to abut against the valve element to cause the valve element to be displaced away from the valve seat against the resilience of the first spring when the stepped piston remains at rest in its operative position;   a fourth pressure chamber formed within the stepped piston on the side of the large diameter portion of the sliding member which is located toward the first pressure chamber;   a path allowing the fourth pressure chamber to communicate with the intensifier third pressure chamber;   a spring chamber formed within the stepped piston on the side of a large diameter portion of the sliding member which is located toward the second pressure chamber;   a second spring disposed within the spring chamber for urging the sliding member toward the first pressure chamber; and   a path allowing the spring chamber to communicate with the atmosphere or a reservoir.   
     
     
       8. A braking unit according to claim 7 wherein seal means are disposed around the outer periphery of each of the large diameter portion and of the small diameter portion of the stepped piston for maintaining a liquid tightness between the stepped piston and an inner peripheral surface of the stepped through-bore formed in the casing, one of the seal means disposed around the outer periphery of either the large or the small diameter portion of the stepped piston including a pair of ring-shaped seal members which are axially spaced apart by a given distance and an outer peripheral portion of the stepped piston which is located intermediate the pair of seal members being in communication with the reservoir through paths formed in the stepped piston and the casing. 
     
     
       9. An intensifier assembly for a vehicle braking unit, the braking unit including a booster connected to a brake pedal to boost a braking liquid when the brake pedal is depressed, a master cylinder connected to the booster to receive the boosted braking liquid from the booster and to generate a pressurized braking liquid for application to a wheel cylinder in response to receiving the boosted braking liquid, said intensifier assembly including: an intensifier unit including: a casing, said casing being shaped to have a large diameter bore, an inlet in fluid communication with said large diameter bore through which pressurized braking liquid from the master cylinder is received, a small diameter bore contiguous with and coaxial with said large diameter bore and an outlet opposite said inlet through which braking liquid is discharged from said small diameter bore to the wheel cylinder;   a movable, stepped piston disposed in a liquid tight manner in said casing, said piston having a large diameter section disposed in said casing large diameter bore, a front end formed by said piston large diameter section, said front end located adjacent said casing inlet, a small diameter section integral with and coaxial with said large diameter section and located partially in said casing large diameter bore and partially in said casing small diameter bore, a rear end formed by said piston small diameter section, said read end being located adjacent said casing outlet;   an intensifier spring extending between said casing and said piston for urging said piston front end toward said casing inlet; and   an intensifier pressure chamber defined in said casing large diameter bore so as to be positioned around said piston small diameter section; and   a communications passageway formed in said casing for connecting said intensifier pressure chamber with the boosted braking liquid from the booster; and     a control valve disposed in said piston for controlling actuation of said piston, said control valve including: a fluid passageway formed in said piston so as to extend between said piston front end and said piston rear end so as to allow braking liquid flow through said piston;   a valve member slidably movable in said piston, said valve member having a valve seat disposed in said fluid passageway that is movable between a open position for allowing braking liquid flow through said fluid passageway and a closed position that blocks braking liquid flow through said fluid passageway;   a control valve pressure chamber formed in said piston around said valve member by at least one surface of said valve member, said control valve pressure chamber including a fluid communication path for connecting said control valve pressure chamber with said intensifier pressure chamber so that said control valve pressure chamber can receive the boosted braking liquid from said intensifier pressure chamber, said pressure chamber being positioned so that when the boosted braking liquid is applied thereto, said valve member is urged towards said valve seat open position; and   a control valve spring disposed in said piston and positioned against said valve member for urging said valve member towards said valve seat closed position, said control valve spring being configured to operate in opposition to the force imposed by the boosted braking liquid in said control valve pressure chamber so that when the force of the boosted braking liquid falls, said control valve spring urges said valve member to said valve seat closed position.     
     
     
       10. The intensifier assembly of claim 9, wherein said intensifier unit spring is located in said intensifier pressure chamber. 
     
     
       11. The intensifier assembly of claim 9, wherein said intensifier unit spring extends between a surface of said casing defining said small diameter bore and said piston small diameter section. 
     
     
       12. The intensifier assembly of claim 3, wherein said intensifier unit valve seat is a ball mounted to said valve member. 
     
     
       13. An intensifier assembly for a vehicle braking unit, the braking unit including a booster connected to a brake pedal to boost a braking liquid when the brake pedal is depressed, a master cylinder connected to the booster to receive the boosted braking liquid from the booster and to generate a pressurized braking liquid for application to a wheel cylinder in response to receiving the boosted braking liquid, said intensifier assembly including: an intensifier unit including: a casing, said casing being shaped to have a large diameter bore, an inlet in fluid communication with said large diameter bore through which pressurized braking liquid from the master cylinder is received, a small diameter bore contiguous with and coaxial with said large diameter bore and an outlet opposite said inlet through which braking liquid is discharged from said small diameter bore to the wheel cylinder;   a movable, stepped piston disposed in a liquid tight manner in said casing, said piston having a large diameter section disposed in said casing large diameter bore, said piston large diameter section and said casing forming a first pressure chamber in said casing large diameter bore that is in fluid communication with said casing inlet, a small diameter section integral with and coaxial with said large diameter section, said piston small diameter section and said casing forming a second pressure chamber in said casing small diameter bore that is in fluid communication with said casing outlet;   an intensifier spring extending between said casing and said piston for urging said piston towards said casing inlet;     a control valve disposed in said piston for controlling actuation of said piston, said control valve including: a first fluid passageway formed in said piston so as to extend between said first pressure chamber and said second pressure chamber so as to allow braking liquid flow through said piston;   a valve member slidably movable in said piston between a first position distal from said casing inlet and a second position proximal to said casing inlet;   a third pressure chamber formed in said piston around said valve member by at least one surface of said valve member and connected to receive boosted braking liquid from the booster, said third pressure chamber being positioned so that when the boosted braking liquid is applied thereto, said valve member is urged towards said first position;   a spring chamber formed in said piston around said valve member by at least one surface of said valve member, said spring chamber including a second fluid passageway in through which the braking liquid in said second pressure chamber can flow into said spring chamber and act in opposition to the braking liquid in said third pressure chamber;   a control valve spring disposed in said spring chamber for urging said valve member towards said second position, said control valve spring being configured to operate in opposition to the force imposed by the boosted braking liquid in said third pressure chamber so that when the force of the boosted braking liquid falls, said control valve spring urges said valve member to said second position; and   a first valve seat attached to said valve member so as to move in unison with said valve member and selectively positioned in said first fluid passageway whereby, when said valve member is in said first position, said first valve seat allows braking liquid flow through said first fluid passageway and when said valve member is in said second position, said first valve seats blocks fluid flow through said first fluid passageway; and   a second valve seat attached to said valve member so as to move in unison with said valve member and selectively positioned in said second fluid passageway whereby, when said valve member is in said first position, said second valve seat blocks braking liquid flow through said second fluid passageway to said spring chamber and when said valve member is in said second position, said second valve seat allows braking liquid flow from said second pressure chamber through said second fluid passageway to said spring chamber.     
     
     
       14. The intensifier assembly of claim 13, wherein said intensifier unit spring extends between a surface of said casing defining said small diameter bore and said piston small diameter section. 
     
     
       15. The intensifier assembly of claim 14, wherein said intensifier unit valve seat is a ball mounted to said valve member. 
     
     
       16. The intensifier assembly of claim 13, wherein said intensifier unit valve seat is a ball mounted to said valve member. 
     
     
       17. An intensifier assembly for a vehicle braking unit, the braking unit including a booster connected to a brake pedal to boost a braking liquid when the brake pedal is depressed, a master cylinder connected to the booster to receive the boosted braking liquid from the booster and to generate a pressurized braking liquid for application to a wheel cylinder in response to receiving the boosted braking liquid, said intensifier assembly including: an intensifier unit including: a casing, said casing being shaped to form a stepped bore having a large diameter section and a small diameter section coaxial with said large diameter section, an inlet in fluid communication with said large diameter bore through which the pressurized braking fluid from the master cylinder is received and an outlet opposite said inlet through which pressurized braking liquid is discharged to the wheel cylinder;   a movable, stepped piston disposed in said casing bore, said piston having a large diameter section disposed in said casing bore large diameter section and a small diameter section partially disposed in said casing small diameter section and partially disposed in said casing large diameter section, said piston being dimensioned to form a first pressure chamber in said casing large diameter bore adjacent said casing inlet, a second pressure chamber in said casing small diameter bore located adjacent said casing outlet and a third pressure chamber in said casing large diameter bore around a portion of said small diameter section that extends into said large diameter bore; and   a spring in said casing bore for urging said piston towards said casing inlet; and     a control unit for regulating displacement of said intensifier unit piston, said control unit including: a fluid passageway formed in said piston so as to provide fluid communication between said first and second intensifier unit pressure chambers;   a control valve disposed in said fluid passageway and being positioned so that when said piston is located adjacent said casing inlet, said control valve allows braking liquid flow through said fluid passageway and when said piston is displaced from away from said casing inlet, said control valve slows braking liquid flow through said fluid passageway and then closes said fluid passageway so as to block fluid flow therethrough;   a switching valve connected at one end to said master cylinder for receiving the pressurized braking liquid therefrom and at an opposed end to said intensifier unit to said intensifier unit third pressurized chamber, said switching valve having a first position for allowing braking liquid flow from the master cylinder to said intensifier unit third pressure chamber and a second position selectively connecting said intensifier unit third pressure chamber to a low-pressure exhaust port;   a pressure-responsive connector between said switching valve body and the booster for receiving the boosted braking liquid from the booster, whereby when said boosted braking liquid is received, said connector holds said switching valve in said first position; and   a biasing spring connected to said switching valve for moving said switching valve to said second position when pressure of the boosted braking liquid falls.     
     
     
       18. The intensifier assembly of claim 17, wherein said intensifier unit spring is located in said intensifier unit third pressure chamber. 
     
     
       19. The intensifier assembly of claim 17, wherein said control unit control valve includes: a valve body disposed in said fluid passageway; a valve seat surface formed around said fluid passageway adjacent said valve body; a standoff post formed integrally with said intensifier unit casing, said standoff post being positioned to extend into said fluid passageway so as to hold said valve body away from said valve seat when said piston is located adjacent said casing inlet. 
     
     
       20. The intensifier assembly of claim 19, wherein said valve body of said control unit control valve is positioned in said fluid passageway to move relative to said intensifier unit casing and said intensifier unit piston and said control valve further includes a valve spring for urging said valve body towards said valve seat.